1. Field of the Invention
The present invention relates to a nonaqueous electrolyte battery, a battery pack and a vehicle provided with the nonaqueous electrolyte battery.
2. Description of the Related Art
In nonaqueous electrolyte batteries, lithium ions are transferred between a negative electrode and a positive electrode to charge and discharge. These nonaqueous electrolyte batteries have been researched and developed as high-energy density batteries.
Nonaqueous electrolyte batteries using a lithium-transition metal composite oxide as a positive electrode active material and a carbonaceous material as a negative electrode active material have already been commercialized. Generally, Co, Mn, Ni or the like is used as the transition metal component of the lithium-transition metal composite oxide.
A nonaqueous electrolyte battery using a lithium-titanium oxide as the negative electrode active material has been recently put to practical use. The lithium-titanium oxide has a lithium ion absorption potential of about 1.55V vs Li/Li+, which is higher than that of a carbonaceous material. A lithium-titanium oxide is reduced in the variation of volume associated with charge and discharge and is therefore superior in cycle performance. Also, lithium ions are inserted in and released from the lithium-titanium oxide by a reaction that no lithium metal is precipitated on the negative electrode and therefore, it enables charge under a large current. Specifically, a rapid charge can be performed.
Since lithium-titanium oxide has a lithium ion absorption potential of as high as about 1.55V (vs Li/Li+), a protective film is hardly formed on the surface of a negative electrode. Consequently, incidence of self-discharge increases.
1,3-propene sultone is added to the nonaqueous electrolytic solution in JP-A 2002-329528 (KOKAI) in order to suppress self-discharge. JP-A 2002-329528 (KOKAI) also describes adding boron-containing compounds such as trimethylsilyl borate to the nonaqueous electrolytic solution.
However, since the protective film formed on the negative electrode by the nonaqueous electrolytic solution according to JP-A 2002-329528 (KOKAI) has high resistance, large current performance is impaired.
On the other hand, JP-A 2004-342607 (KOKAI) describes an effect for preventing reductive decomposition of the nonaqueous electrolytic solution at the negative electrode with a phosphoric ester compound having a silyl.
However, since reduction resistance of the nonaqueous electrolytic solution according to JP-A 2004-342607 (KOKAI) is not sufficient, cycle life of the nonaqueous electrolyte battery decreases.